The present invention relates to a controller for an internal combustion engine and a method for controlling an internal combustion engine.
Japanese Laid-Open Patent Publication No. 2010-265817 discloses one example of a controller for an internal combustion engine that variably sets a closing timing of an intake valve. Particularly, paragraph “0038” of the publication describes control that retards the valve closing timing from a timing at which a piston reaches the bottom dead center (hereafter, referred to as “the bottom dead center timing”). The control is performed when the internal combustion engine is in a predetermined running state.
As described above, when the closing timing of an intake valve is retarded from the bottom dead center timing, some of the mixture of air and fuel in the combustion chamber returns to the intake passage before the intake valve closes. In this case, the returned mixture flows into the combustion chamber in the next combustion cycle. In a constant state in which the amount of returned fuel is constant, a fuel amount necessary for controlling the air-fuel ratio in a mixture that is burned in the combustion chamber to a target value corresponds to the amount of air in the mixture. However, in a transition state in which the returned fuel amount changes due to, for example, change in the valve closing timing, if air-fuel ratio control is performed based on the fuel amount corresponding to the air amount described above, the controllability of the air-fuel ratio may be adversely affected.